Abstract
The Markov decision process is the mathematical formalization underlying the modern field of reinforcement learning when transition and reward functions are unknown. We derive a pseudo-Boolean cost function that is equivalent to a K-spin Hamiltonian representation of the discrete, finite, discounted Markov decision process with infinite horizon. This K-spin Hamiltonian furnishes a starting point from which to solve for an optimal policy using heuristic quantum algorithms such as adiabatic quantum annealing and the quantum approximate optimization algorithm on near-term quantum hardware. In arguing that the variational minimization of our Hamiltonian is approximately equivalent to the Bellman optimality condition for a prevalent class of environments we establish an interesting analogy with classical field theory. Along with proof-of-concept calculations to corroborate our formulation by simulated and quantum annealing against classical Q-Learning, we analyze the scaling of physical resources required to solve our Hamiltonian on quantum hardware.
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Acknowledgments
This work was authored in part by the National Renewable Energy Laboratory (NREL), operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. This research used Ising, Los Alamos National Laboratory’s D-Wave quantum annealer. Ising is supported by NNSA’s Advanced Simulation and Computing program. The authors would like to thank Scott Pakin and Denny Dahl.
Funding
This work was supported by the Laboratory Directed Research and Development (LDRD) Program at NREL. This material is based in-part upon work supported by the National Science Foundation under Grant No. PHY-1653820.
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Jones, E.B., Graf, P., Kapit, E. et al. K-spin Hamiltonian for quantum-resolvable Markov decision processes. Quantum Mach. Intell. 2, 12 (2020). https://doi.org/10.1007/s42484-020-00026-6
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DOI: https://doi.org/10.1007/s42484-020-00026-6